bnxt_en: Do not read the PTP PHC during chip reset

During error recovery or hot firmware upgrade, the chip may be under
reset and the PHC register read cycles may cause completion timeouts.
Check that the chip is not under reset condition before proceeding
to read the PHC by checking the flag BNXT_STATE_IN_FW_RESET.  We also
need to take the ptp_lock before we set this flag to prevent race
conditions.

We need this logic because the PHC now will stay registered after
bnxt_close().

Reviewed-by: Pavan Chebbi <pavan.chebbi@broadcom.com>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>